In diesel and lean burn engines, particulate matter such as, for example, soot is present in exhaust gas from the engine at higher levels than normal gasoline engines. Under these conditions, i.e., higher levels of soot, manufacturers generally choose particulate filters to capture particulate matter. Particulate filters used to remove particulate matter from the exhaust gases of diesel engines are commonly called diesel particulate filters. Accumulated particulate matter such as soot within the filter may eventually reach an undesirable level and may, at this point, cause an undesirable drop in pressure across the diesel particulate filter. Undesirable levels of particulate matter in the DPF may necessitate a regeneration of the filter which may be, generally accomplished with an increase in temperature of exhaust gases to around 600° C. and above just prior to the exhaust gases entering the diesel particulate filter. At these temperatures, the exhaust gas may react with the soot, creating an exothermic reaction to oxidize or burn the soot away which increases the temperatures within the filter, enhancing the burning of the soot, as the soot is burned away.
One method of achieving regeneration temperatures is to increase the idle speed of the engine. However, there are times when such an option is not available or practical such as, for example, when vehicle operations demand a lower engine speed than that required for regeneration when exhaust gas temperature is dependent upon elevated engine speeds.